Electric veneer lathe

ABSTRACT

Embodiments of an electric linear actuator may include a roller screw assembly, an electric motor coupled to the roller screw assembly, and a linear transducer operatively coupled with the roller screw assembly. The motor may be configured to drive the roller screw assembly to extend and retract another component, such as a rod. In some embodiments, the linear transducer may be configured to detect a position of the rod. The roller screw assembly may be coupled directly to the motor via a gear coupling, with the motor disposed generally in axial alignment with the roller screw assembly. Other embodiments disclosed herein include a veneer lathe carriage with electric linear actuators and corresponding apparatuses, methods, and systems.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/462,566 filed Mar. 17, 2017, which is a divisional of U.S. patentapplication Ser. No. 14/882,261 filed Oct. 13, 2015, which claims thebenefit of U.S. Provisional Patent Application No. 62/063,948, filedOct. 15, 2014 and U.S. Provisional Patent Application No. 62/076,432,filed Nov. 6, 2014, both titled “Electric Veneer Lathe,” the entiredisclosures of which are incorporated by reference herein.

BACKGROUND

Conventional rotary veneer lathes and many other machine centers rely onhydraulic actuators for positioning of various components. For example,rotary veneer lathe carriages typically include several hydrauliccylinders that are selectively actuable to move the carriage back andforth. However, hydraulic actuators have some disadvantages. Usinghydraulic fluid compression to reposition veneer lathe carriages cancause variations in peeling thicknesses, which may result insub-standard veneer quality. The use of hydraulic systems may alsopresent environmental concerns, such as oil leaks and soilcontamination, and such systems may require frequent maintenance andrepair.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be readily understood by the following detaileddescription in conjunction with the accompanying drawings. Embodimentsare illustrated by way of example and not by way of limitation in thefigures of the accompanying drawings.

FIGS. 1A-1B illustrate perspective views of an electric linear actuator;

FIGS. 2A-2B illustrate schematic side elevational and bottom views,respectively, of an electric linear actuator;

FIGS. 3A-3G illustrate sectional views taken along corresponding linesof FIGS. 2A-2B;

FIGS. 3H and 3J illustrate sectional views taken along correspondinglines of FIG. 3G;

FIGS. 3K-L illustrate schematic three-dimensional and sectional views ofan electric linear actuator;

FIGS. 4A-B illustrate schematic side elevational views of veneer lathesystems;

FIG. 5 illustrates a perspective view of a veneer lathe carriage withelectric linear actuators;

FIGS. 6A-6B illustrate partial perspective views of the veneer lathecarriage of FIG. 5;

FIG. 7 illustrates a plan view of a veneer lathe carriage with electriclinear actuators;

FIG. 8 illustrates a front elevational view of a veneer lathe carriagewith electric linear actuators;

FIGS. 9A-9C illustrate sectional views taken along corresponding linesof FIG. 8; and

FIG. 10 shows a schematic front elevational view of components of aveneer lathe, all in accordance with various embodiments.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which are shownby way of illustration embodiments that may be practiced. It is to beunderstood that other embodiments may be utilized and structural orlogical changes may be made without departing from the scope. Therefore,the following detailed description is not to be taken in a limitingsense, and the scope of embodiments is defined by the appended claimsand their equivalents.

Various operations may be described as multiple discrete operations inturn, in a manner that may be helpful in understanding embodiments;however, the order of description should not be construed to imply thatthese operations are order dependent.

The description may use perspective-based descriptions such as up/down,back/front, and top/bottom. Such descriptions are merely used tofacilitate the discussion and are not intended to restrict theapplication of disclosed embodiments.

The terms “coupled” and “connected,” along with their derivatives, maybe used. It should be understood that these terms are not intended assynonyms for each other. Rather, in particular embodiments, “connected”may be used to indicate that two or more elements are in direct physicalor electrical contact with each other. “Coupled” may mean that two ormore elements are in direct physical or electrical contact. However,“coupled” may also mean that two or more elements are not in directcontact with each other, but yet still cooperate or interact with eachother.

For the purposes of the description, a phrase in the form “A/B” or inthe form “A and/or B” means (A), (B), or (A and B). For the purposes ofthe description, a phrase in the form “at least one of A, B, and C”means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).For the purposes of the description, a phrase in the form “(A)B” means(B) or (AB) that is, A is an optional element.

The description may use the terms “embodiment” or “embodiments,” whichmay each refer to one or more of the same or different embodiments.Furthermore, the terms “comprising,” “including,” “having,” and thelike, as used with respect to embodiments, are synonymous.

In exemplary embodiments, a computing device may be endowed with one ormore components of the disclosed apparatuses and/or systems and may beemployed to perform one or more methods as disclosed herein.

Most conventional veneer lathes and chargers are driven by hydraulics.However, hydraulic actuation generally requires more power thanactuation of electrical components. More recently, electric drivesystems with roller screw mechanisms have been installed in conventionalveneer lathes. In the prior electric drive systems, an electric motordrives an endless belt that is coupled with a roller screw assembly. Thebelt is driven in a direction generally perpendicular to thelongitudinal center axis of the roller screw assembly. Thus, the motoris vertically, laterally, or vertically and laterally offset from thelongitudinal center axis of the screw assembly.

One of the major disadvantages of this prior configuration is that thebelt tends to fail, due in part to debris that falls onto the beltduring normal operation of the veneer lathe. Another disadvantage ofconventional configurations is that the offset arrangement of the motorrelative to the roller screw mechanism necessitates the use of anencoder to track the position of the piston. If power is losttemporarily, the roller screw must be rotated to a terminal position inorder to reset the encoder.

Finally, in many conventional veneer lathes, the carriage is positionedby a pair of actuators. Whether the actuators are hydraulic cylinders orelectric actuators with offset motors, one actuator follows the other.The “master” actuator is directly controlled, and the “slave” actuatorfollows the master actuator. Positioning errors often arise due to lagor overshoot by the slave. Such errors can become very costly in termsof veneer quality, production speed, equipment maintenance, anddowntime.

The present description provides embodiments of an electric linearactuator, a veneer lathe carriage with one or more electric linearactuators, an electric veneer lathe, and corresponding methods andsystems. For clarity, the term “electric linear actuator” is used inreference to embodiments of the present disclosure, while terms such as“conventional” or “existing” are used in reference to prior actuators,whether electric, hydraulic, pneumatic, etc.

In various embodiments, an electric linear actuator may include a rollerscrew assembly, a motor (e.g., a servo motor) coupled to the rollerscrew assembly, and a linear transducer operatively coupled with theroller screw assembly. The motor may be configured to drive the rollerscrew assembly to extend and retract another component, such as a rod.In some embodiments, the linear transducer may be configured to detect aposition of a portion of the roller screw assembly and/or an extendablerod coupled with the roller screw assembly. In some embodiments, theroller screw assembly may be coupled directly to the motor via acoupling. Optionally, the motor may be disposed generally in axialalignment with the roller screw assembly. In some embodiments, the motoris an AC servo motor coupled directly to a roller screw assembly via agear coupling.

In various embodiments, the roller screw assembly may include a screwshaft and a nut. The nut may include a plurality of rollers arrangedaround, and in axial alignment with, the roller screw. The rollers,screw shaft, and/or nut may have complementary thread profiles, suchthat rotation of the screw shaft by the motor causes the nut to movealong the screw shaft. In various embodiments, the roller screw assemblymay be, or may include, a planetary roller screw.

In various embodiments, the motor may include a position sensorconfigured to measure degrees of rotation. In some embodiments theposition sensor may be a rotary electrical transformer or rotaryposition transducer (e.g., a multi-turn resolver). The position sensorof the motor and/or the linear transducer may be coupled with acontroller. The controller may be configured to track the position ofthe nut/rod based on data from the position sensor and/or the lineartransducer. Optionally, the controller may be configured to use thereceived data to measure ‘give’ or backlash. In some embodiments, thecontroller may be configured to use the received data to determine thatthe electric linear actuator needs immediate maintenance, and/or torecommend a timeframe for maintenance. For example, the nut may requirea small amount of clearance within the roller screw assembly. Thecontroller may be configured to determine how much angular motion in themotor is required before the linear transducer detects a change in theposition of the nut, to assess the condition of the nut (e.g., degree ofwear) based on that determination, and to provide a correspondingrecommendation for current or future maintenance. The provision ofpredictive maintenance recommendations by the controller may help toextend the useful life of the electric linear actuator. Similarly, thecontroller may be configured to recommend one or more adjustments toother system components based on the data.

In some embodiments the electric linear actuator may include atemperature sensor positioned to detect a temperature of the nut, thescrew shaft, or both. Optionally, the temperature sensor may be aninfra-red (IR) sensor. The temperature sensor may be operatively coupledto the controller. The controller may be configured to monitor thecondition of the roller screw assembly based on data from thetemperature sensor. The controller may also be configured to recommendand/or implement a corrective action based on the data. For example, thecontroller may be configured to compare a detected temperature to adesired temperature range. Based on the comparison, the controller mayincrease or decrease a flow of lubricant into the roller screw assembly,shut down the motor (e.g., if the temperature exceeds the upper end ofthe desired temperature range), recommend shutdown/maintenance, or thelike.

Optionally, the controller may be operatively coupled with one or moresensors configured to detect a position of another component. Thecontroller may be configured to control one or more electric linearactuators based at least in part on the detected position. In someembodiments, the electric linear actuators may be coupled with acontroller programmed to control both of the electric linear actuatorsas slaves based on a “virtual master.” For example, the controller maybe configured to control the electric linear actuators based on theposition of another component (e.g., data from an encoder on the lathespindle). Optionally, the controller may include a secondary drivecontroller that is operable to synchronize the actuation of bothelectric linear actuators to reduce or eliminate position errors.

The threaded rollers of the roller screw assembly may provide moreprecise positioning than hydraulic or ball screw and nut components. Thethreaded rollers may also offer a larger load transfer contact surface,significantly increasing burden capacity and longer life. Coupling themotor and the roller screw design directly, rather than by way of abelt, may reduce or eliminate the loss in precision that is typical ofbelt-driven roller screw actuators. In comparison to conventionalhydraulic actuator systems, which require a complex support system ofvalves, pumps and filters, embodiments described herein may be morecompact, robust, and/or energy-efficient than conventional actuators. Assuch, embodiments of electric linear actuators may require less frequentand/or less complicated maintenance than conventional actuator systems.In various embodiments, an electric linear actuator may be provided as areplacement for an existing conventional actuator, such as a hydrauliccylinder or ball screw actuator.

Electric linear actuators may be used in a variety of applications. Forexample, a veneer lathe carriage may be provided with one or more one ormore electric linear actuators that are collectively operable toreposition the carriage. In some embodiments, two electric linearactuators may be positioned at generally opposite ends of the carriage.In some embodiments, the electric linear actuators may be coupled with acontroller programmed to control both of the electric linear actuatorsbased at least on data received from the linear transducer and/or theposition sensor of the motor. The controller may be configured to detectcarriage position/skew. In various embodiments, the controller may beprogrammed to control the electric linear actuators as slaves, based ona virtual master geared to the position of a reference component. Forexample, the virtual master may be geared to the lathe spindle, suchthat the electric linear positioners are controlled as a function oflathe spindle position (e.g., based on data from an encoder that detectsthe position and/or rotational velocity of the lathe spindle).Optionally, the controller may include a programmable logic controller(PLC) and a secondary controller operatively coupled with the PLC. Theelectric linear actuators may be controlled by the secondary drivecontroller based on data from the motors, and the PLC may sendinstructions to the secondary drive controller based on data receivedfrom the temperature sensors and linear transducers.

Therefore, embodiments of veneer lathe carriages with electric linearactuators generally as described herein may provide more consistent peelthickness for higher quality veneer. Embodiments of a veneer lathecarriage with electric linear actuators as described herein may providemuch higher cycle rates in both peel and retract functions,significantly increasing veneer production. Moreover, coupling thelinear transducers (e.g., Temposonic® probes) to the knife bar may helpto prevent carriage skew by effectively reporting actual knife locationimmediately after planned or un-planned power interruption, without the‘homing’ procedure required in conventional systems after a powerinterruption. In various embodiments, the electric linear actuators maybe configured to retract the lathe carriage at a rate of at least 20inches per second. Optionally, the electric linear actuators may beconfigured to retract the lathe carriage at a rate of up to 25 inchesper second, or at a faster rate. In addition, using electric linearactuators in place of conventional actuators may reduce or eliminate thebacklash typically caused by varying fiber density.

In some embodiments, a method of upgrading an existing machine (e.g., aveneer lathe carriage) may include removing one or more existingactuators from the machine and operatively coupling one or more electriclinear actuators with the machine. Optionally, the electric linearactuator(s) may be installed at the location formerly occupied by theexisting actuator(s). Again, the electric linear actuator(s) may includea motor, a roller screw assembly directly coupled to the motor, and alinear transducer coupled with the roller screw assembly. The motor maybe positioned generally in axial alignment with the roller screwassembly.

In various embodiments, an electric linear actuator may be adaptable toany brand or type of machine that has conventional linear actuators(e.g., any brand or type of veneer lathe, cutting device, conveyor,stacker, log turner, etc.). Therefore, embodiments described herein mayprovide a relatively simple method of upgrading an existing machine withfew or no modifications to the machine other than the removal of some orall of the components of a conventional actuator. Benefits of such anupgrade may include lower horsepower requirement, less costly operation,and/or reduced maintenance.

Those with ordinary skill in the art will readily appreciate thatelectric linear actuators may also be used in a variety of othermachines and applications. Therefore, while the present disclosuredescribes veneer lathe carriages with electric linear actuators by wayof illustration, these examples are not intended to be limiting. Othermachines with electric linear actuators, methods of upgrading othermachines to replace conventional actuators with electric linearactuators, and corresponding methods of use are specificallycontemplated herein.

FIGS. 1A-1B illustrate perspective views of an electric linear actuator100, in accordance with various embodiments. Electric linear actuator100 may include a motor 102, a roller screw assembly 110, and a lineartransducer assembly 120. Motor 102 may be coupled with a proximal end ofroller screw assembly 110 by a coupler 104. A rod assembly 106 may becoupled with a distal end of roller screw assembly 110. Roller screwassembly 110 and/or rod assembly 106 may be at least partially containedwithin a housing 108. Linear transducer assembly 120 may be coupled toroller screw assembly 110. Optionally, linear transducer assembly 120may be positioned below roller screw assembly 110 generally betweenmotor 102 and a distal end of the electric linear actuator 100.Optionally, a temperature sensor 112 may also be coupled to roller screwassembly 110. In some embodiments, linear transducer assembly 120 andtemperature sensor 112 may be disposed on opposite sides of roller screwassembly 110.

In various embodiments, motor 102 may be a servo motor. In someembodiments motor 102 may be an A/C servo motor with an encoder/resolverand a servo drive. Alternatively, motor 102 may be any other suitableelectric motor.

Coupler 104 may be a gear coupling. In some embodiments, coupler 104 maybe a double engagement, close coupled type of gear coupling (e.g., FALK™Type G20). In other embodiments, coupler 104 may be a gear-type flexiblecoupling, a universal joint, or any other suitable type of rod coupling.

In various embodiments, roller screw assembly 110 may be a planetaryroller screw assembly. Alternatively, roller screw assembly 110 may be aconventional and/or commercially available roller screw mechanism orsuitable substitute thereof. Roller screw assembly 110 may be in axialalignment with motor 102 and rod assembly 106.

In some embodiments, temperature sensor 112 may be an infra-red (IR)temperature sensor. In other embodiments, temperature sensor 112 may beany other suitable type of temperature sensor. Some embodiments may lacktemperature sensor 112. Embodiments of roller screw assembly 110 andlinear transducer assembly 120 are described in further detail below.

FIGS. 2A-2B illustrate schematic side elevational and plan views,respectively, of an electric linear actuator, in accordance with variousembodiments. FIGS. 3A-3G illustrate sectional views taken alongcorresponding lines of FIGS. 2A-2B, FIGS. 3H and 3J illustrate sectionalviews taken along corresponding lines of FIG. 3G, and FIGS. 3K-Lillustrate perspective views of an electric linear actuator, all inaccordance with various embodiments. For clarity, FIG. 3A illustrates asectional view taken along line A-A of FIG. 2A, FIG. 3B illustrates asectional view taken along line B-B of FIG. 2A, and so on.

Roller screw assembly 110 may be operable to convert rotary motion frommotor 102 into linear motion to extend and retract another component,such as a rod, as shown for example in FIG. 2A (extended and retractedpositions of rod assembly 106 indicated in broken lines). Referring nowto FIG. 3G, which shows a side cutaway view of electric linear actuator100, roller screw assembly 110 may include a nut 114 and a screw shaft118 disposed through nut 114. Nut 114 may include a plurality of rollersarranged around, and in axial alignment with, screw shaft 118. Therollers, screw shaft 118, and/or nut 114 may have complementary threadprofiles, such that rotation of the screw shaft by the motor causes thenut 114 to move along screw shaft 118 to extend and retract rod assembly106. In various embodiments, roller screw assembly 110 may be, or mayinclude, a planetary roller screw assembly. Roller screw assemblies areknown in the art and, as such, will not be described further herein.

Optionally, roller screw assembly 110 may include one or more bumpers132 configured to reduce impact force or jarring of nut 114 when rollerscrew assembly is fully extended. Likewise, roller screw assembly 110may include a bumper 134 configured to reduce impact force or jarring ofnut 114 when roller screw assembly is fully retracted.

Referring still to FIG. 3G, linear transducer 120 may include sensor rod122, key block 124, magnet 126 (FIG. 3F), and sensor 128. Sensor rod 122may be coupled with nut 114 via key block 124. Magnet 126 may be mountedto key block 124, and sensor 128 may be coupled with a proximal end ofsensor rod 122. Sensor rod 122 may be disposed through magnet 126 andkey block 124, and key block may be operatively coupled with the rollerscrew assembly. Magnet 126 and key block 124 may be slidable alongsensor rod 122.

In various embodiments, sensor 122 may be a magnetostrictive linearposition sensor. For the purposes of this description, amagnetostrictive linear position sensor is a sensor that measures thedistance between a position magnet (e.g., magnet 126) and one end of asensor rod (e.g., sensor rod 122). In a particular embodiment, lineartransducer 120 is a Temposonics® linear position sensor (MTS SystemsCorporation). In other embodiments, linear transducer 120 may be anothermagnetostrictive linear position sensor, a non-magnetostrictive linearposition sensor, or any other suitable type of linear position sensor.

As best shown in FIG. 2A, the rotation of screw shaft 118 by motor 102may cause nut 114 to move along screw shaft 118, which may causeextension or retraction of rod assembly 106 depending on the directionof rotation. As nut 114 moves along screw shaft 118, key block 124 andmagnet 126 may move along sensor rod 122. Sensor 128 may detect a strainpulse induced in a magnetostrictive waveguide (e.g., in sensor rod 122)by the interaction between the magnetic field of magnet 126 and aninterrogation current pulse applied along the waveguide. Sensor 128 maybe configured to detect the position of magnet 126 as a function ofelapsed time between the application of the interrogation pulse anddetection of the corresponding strain pulse.

Sensor 128 may be operatively coupled with motor 102 and/or a controller136 (FIG. 3G). In some embodiments, motor 102 may include a multi-turnresolver or absolute encoder, or other type of position sensorconfigured to measure degrees of rotation. Motor 102 and/or controller136 may be configured to receive data from linear transducer 120 and todetermine a position of rod assembly 106 based on the received data.

Optionally, controller 136 may be configured to track the position ofthe nut/rod based on data from the position sensor and/or the lineartransducer. In some embodiments, controller 136 may be configured to usethe received data to measure ‘give’ or backlash (e.g., based on thedifference between an expected position of the nut/rod and the actualposition of the nut/rod). In addition, controller 136 may be configuredto use the received data to determine that the electric linear actuatorneeds immediate maintenance, and/or to recommend a timeframe formaintenance. For example, controller 136 may be configured to determinehow much angular motion in motor 102 is required for linear transducer120 to detect a change in the position of nut 114. Based on thatdetermination, controller 136 may assess the condition of nut 114 (e.g.,degree of wear) and provide a corresponding recommendation for currentor future maintenance. The provision of predictive maintenancerecommendations by controller 136 may help to extend the useful life ofthe electric linear actuator 100. Similarly, controller 136 may beconfigured to recommend one or more adjustments to other systemcomponents based on the data from the position sensor, lineartransducer, and/or other sensors.

Temperature sensor 112 may be positioned to detect a temperature of nut114 and/or roller screw 118. For example, in the embodiment shown inFIG. 3G, temperature sensor 112 is positioned to detect a temperature ofnut 114 when nut 114 is near the location of temperature sensor 112, andto detect a temperature of roller screw 118 when nut 114 is further fromtemperature sensor 112. Optionally, temperature sensor 112 may beoperatively coupled to controller 136, and the controller may beconfigured to monitor the condition of the roller screw assembly 110based at least in part on data from the temperature sensor 112. Thecontroller may also be configured to recommend and/or implement acorrective action based on the data. For example, the controller may beconfigured to compare a detected temperature to a desired temperaturerange. Based on the comparison, the controller may increase or decreasea flow of lubricant into the roller screw assembly (e.g., through greasefitting 130), shut down the motor (e.g., if the temperature exceeds theupper end of the desired temperature range), or make recommendations toan operator regarding maintenance. The controller may be provided withan interface configured to display parameters such as backlash,temperature of the nut/roller screw, recommendations, and the like.

Electric linear actuators may be used in a variety of applications inplace of conventional actuators such as hydraulic cylinders. Forexample, a veneer lathe system may be provided with one or more one ormore electric linear actuators that are collectively operable toreposition various components of the system.

FIGS. 4A-B illustrates schematic side elevational views of veneer lathesystems, each including a charger-scanner and a veneer lathe. Thecharger-scanner includes a charger, a scanner, and a pendulum. Typicallythe lathe includes a core drive with at least one roller bar thatprovides motive force to rotate the log, a knife bar assembly mounted ona carriage that is movable toward and away from the rotational axis ofthe log, and spindles that engage the opposite end of the log. In somelathes the spindles may also provide rotational force, while otherlathes may lack spindles.

In operation, logs are fed in succession to the charger-scanner by a logladder, step feeder, or the like. The log is rotated by the chargerwithin the field of view of the scanner, which collects geometricmeasurements and/or other data. Based on the scan data, the log isrepositioned by the charger to an optimal orientation for peeling. Thelog is transferred to the lathe in that orientation by the pendulum. Thelathe rotates the log in the desired orientation. As the log is rotated,the knives are brought into contact with the outer surface of the log topeel the log. As the diameter of the log decreases, the positions of thecarriage and roller bar(s) and the rotational angle (i.e., pitch) of theknives are adjusted as required to continue the peeling process.

The moving components of these devices are operated by correspondingactuators. For example, in the illustrated systems, actuators A and Bare operated to move logs up the log ladder or step feeder and onto thecharger, respectively. Actuators C raise the log for scanning andactuator D moves the pendulum. Actuators E, F, and G of the core driveare operated to reposition the roller bar(s). Actuators H are operatedto move the carriage forward and backward, and actuator I is operated toadjust the pitch of the knives. The number and configuration ofactuators varies among lathe systems. Regardless, precise andcoordinated operation of the system's moving components is required toobtain good quality veneer of substantially uniform thickness.

In conventional veneer lathe systems, these actuators are typicallyhydraulic actuators. Hydraulic actuators are relatively expensive tooperate and maintain. They are also prone to backlash and can producevariable peeling thicknesses. Off-set belt actuators with ball screwdrives, in which the motor and ball screw are vertically or horizontallyparallel and connected by a belt, have also been used to drive lathecarriages. This type of actuator may be prone to belt failures, andrequires a rehoming procedure after a power interruption.

Electric linear actuators as described herein may be used instead of, oras replacements for, conventional actuators in a variety ofapplications. In the context of veneer lathe systems and veneerproduction facilities, electric linear actuators may be used toselectively reposition moving components of log ladders, step feeders,charger-scanners, lathes, and/or other devices. By way of example, FIGS.5-9C illustrate a veneer lathe carriage 200 with electric linearactuators 100, in accordance with various embodiments.

Referring first to FIG. 5, a veneer lathe carriage 200 may include abase 238 configured to support a knife bar assembly 240 with a pluralityof knives 242. In some embodiments, knives 242 may include knife clamps242 a configured to secure a blade 242 b against a backing plate orother component of knife bar assembly 240. In other embodiments, blade242 b and knife clamp 242 a may be integral. In any case, each of theknives 242 may have a cutting edge, and the knives may be arranged withthe cutting edges aligned along an axis. Knife bar assembly 240 may becoupled with, and movable relative to, a frame 244 of a lathe. Invarious embodiments, carriage 200 may include two electric linearactuators 100 coupled with frame 244 with brackets or other fasteners.Electric linear actuators 100 may be positioned at generally oppositeends of knife bar assembly 200.

In some embodiments, the linear transducers may be coupled to the knifebar assembly 240 to allow detection of carriage skew and effectivereporting of the actual locations of the knives 242 immediatelyfollowing planned or un-planned power interruptions. For example, asbest shown in FIGS. 6A-B, the distal end of the each rod 106 may bepivotably coupled to a corresponding trunnion 246, and the trunnions 246may be coupled to corresponding opposite sides of the knife bar assembly240.

Other configurations are also possible, and electric linear actuators asdescribed herein may be used in place of hydraulic and otherconventional actuators on a variety of lathe carriages.

In some embodiments, electric linear actuators 100 may be coupled with acontroller 236. Again, each of the motors 102 may include a positionsensor (e.g., a multi-turn absolute encoder or resolver) configured todetect rotational position/degrees of rotation. Controller 236 may beconfigured to control motors 102 (and thus the position of the carriage)based on data from the position sensors of motors 102, lineartransducers 120, and/or one or more other sensors (e.g., vision sensorspositioned to detect the carriage or knives).

Optionally, as shown by way of example in FIG. 7, controller 236 mayinclude a secondary drive controller 236 a and a primary controller 236b (e.g., a PLC) in electronic communication. Secondary drive controller236 may receive data from the position sensors of the motors 102.Secondary drive controller 236 a may be configured to detect theposition of the knives 242 based on the data from the position sensors(e.g., rotational angle, rotational direction, and number ofrevolutions) and to control motors 102 based at least in part oninstructions from primary controller 236 b.

Primary controller 236 b may receive data from the linear transducers120 and temperature sensors 112. Primary controller 236 b may beconfigured to determine the position of the carriage/knives based on thedata from the linear transducers 120. For example, primary controller236 b may be configured to determine the position of knives 242 based onthe positions of the nuts 114. In this example, linear transducers 120are used as a redundant position detection system, allowing the carriageposition to be tracked even if one or both motors 102 becomes uncoupledfrom the roller screw assembly 110, the motor's position sensor fails,or the secondary drive controller 236 a is removed or becomesinoperable.

One or both of primary controller 236 b and secondary drive controller236 a may be configured to detect carriage skew as well as knifeposition. For example, skew may be detected by comparing the detectedpositions of the nuts 114 or the rotational angle of the screw shafts118. A difference between the positions/angles may be an indication thatone of the rods 106 is extended to a greater distance than the other,resulting in skew. In response to detecting such a difference, theprimary controller 236 b and/or secondary drive controller 236 a mayoperate one or both motors 102 to correct the difference, instruct themotors 102 to cease operation, generate a maintenance recommendation,and/or generate an audible or visual alert.

Optionally, primary controller 236 b may be configured to monitor thecondition of various components, make recommendations for maintenance,and/or halt operation of the linear transducers 100 based on receiveddata. For example, primary controller 236 b may monitor wear in nuts 114based on data received from the secondary drive controller 236 a and/orthe linear transducers 120, such as by tracking the number ofrevolutions of the motor per increment of distance traveled by thecorresponding nut over time. As another example, primary controller 236b may monitor the condition of screw shafts 118 and/or nuts 114, orother components of the electric linear actuators 100, based ontemperature data received from temperature sensors 112. An increase indetected temperature above a predetermined maximum threshold, adifference between the temperatures detected by the two temperaturesensors for a given time point, or a particular pattern of temperaturefluctuation may be indications of wearing or malfunction in one or morecomponents. Based on the monitored parameters, primary controller 236 bmay be configured to generate a maintenance recommendation and/orinstruct the secondary drive controller 236 b to stop the electriclinear actuators to limit damage to the carriage or other components.

The above functions and others may be distributed among secondary drivecontroller 236 a and primary controller 236 b in a variety of differentways. Alternatively, controller 236 may be a single controller (e.g., aPLC) operable to perform some or all of the functions of secondary drivecontroller 236 a and primary controller 236 b.

In some embodiments, controller 236 may be configured to control oneelectric linear actuator 100 based on another, such that one actuator isthe “master” and the other is the “slave.” In other embodiments,controller 236 may be programmed to control both of the electric linearactuators 100 as slaves based on a “virtual master.” The virtual mastermay be a representation of the position or speed of another component.

For example, the virtual master may be functionally geared to therotational speed of the lathe spindles. FIG. 10 shows a schematic frontelevational view of various components of a lathe 300. The lathespindles 350 may be disposed through corresponding holes in the latheframe 344 (see e.g., FIGS. 5 and 6A-B) and coupled with a drive shaft354 by corresponding belts 352. Drive shaft 354 may be coupled to amotor 356 operable to rotate the drive shaft. An encoder 358 may bedisposed within motor 356, positioned along drive shaft 354, orotherwise operatively coupled with one of the lathe spindles 350.Controller 236 may be configured to control the electric linearactuators 100, and thus the forward and backward movement of thecarriage, based at least in part on data from encoder 358 and/or datafrom one or more vision sensors 360 positioned to detect the position ofthe carriage, knives, or other lathe component. Because lineartransducers 120 are coupled to the knife bar assembly 240 via nuts 114,rods 106, and trunnions 246, electric linear actuators 100 may enablethe actual knife location to be determined immediately after a powerinterruption without the ‘homing’ procedure required in conventionalsystems. In various embodiments, electric linear actuators 100 may beconfigured to retract the veneer lathe carriage 200 at a rate of up to25 inches per second or more. In addition, substituting electric linearactuators 100 for conventional actuators may reduce or eliminate thebacklash typically caused by varying fiber density.

In various embodiments, an electric linear actuator may be provided as areplacement for an existing conventional actuator, such as a hydrauliccylinder or ball screw actuator. Thus, a method of upgrading an existingmachine (e.g., a veneer lathe carriage) may include removing one or moreconventional actuators from the machine and operatively coupling one ormore electric linear actuators with the machine. Optionally, theelectric linear actuator(s) may be installed at the location formerlyoccupied by the conventional actuator(s) with little or no modificationof the remaining components of the machine. In some embodiments, themethod may further include coupling a controller with the electriclinear actuator(s), the motor, an optical sensor/scanner, a temperaturesensor, and/or another position sensor. In various embodiments, thecontroller may include a programmable logic controller (PLC), asecondary drive controller, or both.

In other embodiments electric linear actuators can be used instead of(or as replacements for) conventional linear actuators, such ashydraulic or offset-belt ball screw actuators, to reposition othercomponents of veneer lathe systems, including (but not limited to)components of log ladders/feeders, chargers, pendulums, core drives,roller/pressure bars, to adjust knife pitch or height, and the like.Similarly, electric linear actuators can be used instead of (or asreplacements for) conventional linear actuators to move other machinesor machine components. For example, electric linear actuators may beused in place of hydraulic cylinders or other conventional linearpositioners in presses, log turners, slabbers/canters, saws, chippers,profilers, positioning infeeds, positioning pins, stackers, and/or inany other suitable application.

Although certain embodiments have been illustrated and described herein,it will be appreciated by those of ordinary skill in the art that a widevariety of alternate and/or equivalent embodiments or implementationscalculated to achieve the same purposes may be substituted for theembodiments shown and described without departing from the scope. Thosewith skill in the art will readily appreciate that embodiments may beimplemented in a very wide variety of ways. This application is intendedto cover any adaptations or variations of the embodiments discussedherein. Therefore, it is manifestly intended that embodiments be limitedonly by the claims and the equivalents thereof.

What is claimed is:
 1. An electric linear positioning system,comprising: two electric linear positioners, wherein each of theelectric linear positioners independently includes a roller screwassembly, wherein the roller screw assembly includes a nut and a screwshaft disposed through the nut, a motor coupled to a proximal end of theroller screw assembly and in axial alignment with the roller screwassembly, wherein the motor includes a rotary position sensor that isoperable to detect a rotational angle of the screw shaft; and a linearposition sensor coupled to the roller screw assembly, wherein the linearposition sensor is operable to detect a position of the nut; and acontroller programmed with instructions that are operable, uponexecution by a processor, to cause the controller to determine adifference between the detected positions of the nuts or the rotationalangles of the screw shafts based on data received from the linearposition sensors or the rotary position sensors, respectively, andoperate one or both of the electric motors to correct the difference. 2.The electric linear positioning system of claim 1, wherein said rollerscrew assembly includes a planetary roller screw.
 3. The electric linearpositioning system of claim 1, wherein the position sensors aremagnetostrictive linear position sensors.
 4. The electric linearpositioning system of claim 2, wherein the instructions are furtheroperable, upon execution by the processor, to cause the controller tooperate the electric linear positioners based at least in part on aposition or rotational speed of a reference component.
 5. The electriclinear positioning system of claim 4, wherein the reference component isa shaft, and the control system is coupled with an encoder positioned todetect the rotational speed of the shaft.
 6. The electric linearpositioning system of claim 5, wherein the shaft is a drive shaft of alathe spindle.
 7. The electric linear positioning system of claim 1,wherein the controller is configured to estimate an amount of wear inthe nut based at least on data from the corresponding position sensor orthe corresponding encoder or resolver.
 8. The electric linearpositioning system of claim 1, wherein the controller is furtherconfigured to generate a maintenance recommendation based on theestimated amount of wear in the nut.
 9. The electric linear positioningsystem of claim 1, further including a temperature sensor operativelycoupled with the roller screw assembly and the controller, wherein thetemperature sensor is positioned to detect a temperature of one or bothof the nut and the screw shaft, and the controller is further configuredto determine that the detected temperature exceeds a predeterminedmaximum temperature, and in response, generate a maintenancerecommendation or stop the motors.
 10. The electric linear positioningsystem of claim 9, wherein the controller includes a secondary drivecontroller operatively coupled with the encoder or resolver and themotors, and a primary controller operatively coupled to the temperaturesensor, the linear transducers, and the secondary drive controller. 11.A system comprising: a first component that is movable along a motionaxis relative to a frame; and a pair of electric linear positionerscoupled to the first component on opposite sides of the motion axis,each of the electric linear positions of said pair having a roller screwassembly, an electric motor coupled to a proximal end of the rollerscrew assembly and in axial alignment with the roller screw assembly,and a linear position sensor operatively coupled to the roller screwassembly, wherein each of said roller screw assemblies includes arespective nut and a respective screw shaft disposed through the nut,each of said electric motors includes a respective rotary positionsensor operable to detect a rotational position of the respective screwshaft, and each of the linear position sensors is operable to detect aposition of the respective nut; wherein the electric linear positionersare selectively actuable to move the first component along the motionaxis, and wherein the electric linear positioners are operableindependently of one another to correct skew of the first component. 12.The system of claim 11, wherein said roller screw assembly includes aplanetary roller screw and the first component is a carriage.
 13. Thesystem of claim 12, wherein the carriage is a veneer lathe carriage andthe position sensors are magnetostrictive linear position sensors. 14.The system of claim 11, wherein the rotary position sensors are encodersor resolvers, the system further comprising a controller operativelycoupled with the position sensors and configured to operate the electriclinear positioners independently of one another based on data receivedfrom the respective position sensors.
 15. The system of claim 14,wherein the controller is configured to identify the skew based on thedata received from the respective position sensors.
 16. The system ofclaim 14, wherein the first component is a veneer lathe carriage and thecontroller is configured to operate the electric linear positionersbased at least in part on a position or rotational speed of a referencecomponent.
 17. The system of claim 16, wherein the reference componentis a drive shaft of a lathe spindle, and the controller is operativelycoupled with an encoder positioned to detect the rotary speed of thelathe spindle.
 18. The system of claim 14, wherein the controller isconfigured to estimate an amount of wear in the nuts based at least ondata from the corresponding position sensors or the correspondingencoders or resolvers.
 19. The system of claim 18, wherein thecontroller is further configured to generate a maintenancerecommendation based on the estimated amount of wear in the nut.
 20. Thesystem of claim 14, wherein each of the electric linear positioners ofsaid pair further includes a temperature sensor operatively coupled withthe roller screw assembly and the controller, and wherein the controlleris further configured to determine that the detected temperature exceedsa predetermined maximum temperature, and in response, generate amaintenance recommendation or stop the motors.